1. Field of the Invention
The field of the invention is that of modems for transmitting digital signals and especially spread spectrum modems. To be more precise, the present invention concerns a spread spectrum transmission system in which digital signals are transmitted between a transmitter and a receiver and spectrum spreading is achieved by pseudorandom encoding of the wanted information to be transmitted. The invention applies in particular to military applications in microwave telecommunications.
2. Description of the Related Art
In military applications spread spectrum operation is usually adopted for ECCM (Electronic Counter-CounterMeasures) and entails multiplying the wanted signal to be transmitted by a code called the spreading code or sequence obtained from a pseudorandom generator whose clock frequency is much higher than the maximal frequency of the wanted signal. The number of wanted information bits transmitted per Hz is therefore very small.
FIG. 1 shows a timing diagram explaining the principle of spectrum spreading by means of a spreading sequence.